The present invention relates to rating monitoring devices and applies in particular to vehicles as well as to any devices in which the physical parameters or quantities vary conjointly.
The car industry provides some simple examples of rating monitors, in particular speedometers and revolution counters which both simply virtually instantaneous information. There is a tendency nowadays to give the user more elaborate information, taken as a mean value, that is to say integrated over a certain time interval. An example of this is the mean consumption or mean speed. This tendency is apparent not only with regard to vehicles but also with regard to other mass-produced and/or widely distributed products or devices.
This need can be satisfied by means of electronic devices generally comprising two input circuits which emit signals each representative of physical quantities which vary conjointly, such as for example, the distance travelled, the fuel consumption, the number of revolutions of an engine, or the time, as well as processing means for continually determining the rate of change of one of the physical quantities relative to the other.
One particular problem arises in practice. By nature of the operation, mean operation must entail a significant initial advance of the relevant physical quantities to allow the insignificant or undesireable fluctuations to disappear. A large storage capacity is therefore needed to keep a record of this initial advance.
Unfortunately, this increases both the complexity and the cost price of the devices used, and these two factors are important in the mass-production of widely distributed articles. Real problems are encountered in the choice of a practical compromise.
Another difficulty which is added to the first one lies in the fact that digital electronic devices have sequential operation. As mentioned above, the mean has to be produced over long time intervals so as to allow any inadvertent fluctuations in the relevant physical quantities to disappear. On the other hand, it is desirable to renew the result indicated after short time intervals so as to avoid discontinuity in the result, which is just as disagreeable for the user.